Method and apparatus to separate coverage limited and co-channel limited interferences

ABSTRACT

Coverage and usage-based limitations to a wireless communications network can be estimated by monitoring network performance during a periods in which the network is relatively busy and relatively non-busy. For example, differences in distributions of bit error rates for calls in such time periods can be used to assess whether network limitations are associated with reduced-coverage zones or are usage-based. Such estimates can be used to target specific network features that limit network performance.

This application is a continuation of U.S. patent application Ser. No.11/638,240, now U.S. Pat. No. 9,113,362, which is herein incorporated byreference in its entirety.

FIELD

The disclosure pertains relates to network diagnostics for wirelesscommunication networks.

BACKGROUND

Wireless communication networks are currently used for a broad range ofbusiness and personal communications needs. Wireless network subscribershave grown accustomed to ready access to telephone, messaging, and dataservices regardless subscriber location or subscriber travel. Because ofthe increased reliance of subscribers on wireless networks, subscribersinsist on services being available at all times at any arbitrarylocation. Unfortunately, network design can occasionally be inadequateto provide a requested service, frustrating network subscriber.

While network operators have long emphasized providing reliable servicesto their subscribers, diagnosing the reasons for any particularcommunication problem is difficult. In many wireless networks, droppedcalls or other missed or incomplete data or voice communications areassociated with limitations to network coverage. Limited coverageproblems arise because of local topography (e.g., hills) or structures(office towers) that block or obscure some portions of a coverage area(typically one or more cells) from receiving suitable radio signals froma network radio tower or other transmitter. In some cases, towerplacement is less than ideal because of an inability to secure necessaryproperty permissions, or any of a variety of other practical orpolitical reasons result in cell towers unavoidably being placed inlocations that provide less than optimum continuous coverage. Thus,“holes” in coverage are creates in which subscriber mobile stations areeither too far away from cell towers or are blocked or partially blockedfrom cell towers by terrain or buildings. These holes appear as deadspots where mobile stations are unable to acquire a sufficient signal tosustain two-way communications. A user of a mobile station entering oneof these holes while engaged in a call will often experienceprogressively worsening signal reception, resulting in eitherdisruptions in communications or call termination.

Other communications problems are associated with a number ofsubscribers using the network or requesting network services. Forexample, in some wireless networks, unique sets of radio frequencies areassigned to each base station. Because only a finite number offrequencies are available, frequencies are used at multiple basestations and are generally allocated according to frequency reuse plansin order to avoid different signals on the same frequency from appearingat the same transmitter or receiver. Although an ideal frequency reuseplan can be derived from propagation models, such a plan is onlyeffective to the extent cell arrangement reflects an idealized layoutwhere each cell is spaced according to a uniform honeycomb pattern, withall cells having the same geographic elevation and flat topography. Inpractice, cells are irregularly shaped and spaced, yielding to thevarying nature of terrain and the practicalities of securing suitablebase station locations. Even an ideal layout cannot prevent more thanone radio signal at a common frequency from appearing in a particularcell, but merely provides reduced amplitudes of any unwanted radiofrequency signals. Thus, so-called co-channel interference arises whentwo or more different transmitting stations (mobile or stationary) inrelatively proximate areas both use the same radio frequency channel.Like holes in coverage, co-channel interference can produce degradedsignal reception or call termination.

Network operators strive to prevent dropped calls and other missedcommunications due to limited network coverage or excess communicationdemand. For holes in geographic coverage, wireless operators can installadditional transmitter or change a location or transmission direction ofan existing transmitter. Co-channel interference effect can be reducedbase on, for example, adjustments to a frequency reuse plan. However,for such modifications to be effective, the source of any communicationslimitations should be identified as being associated with coveragedeficiencies or capacity limits. Conventional methods of assessingnetwork performance are based on drive tests in which atransmitter/receiver is driven through a network coverage area. Suchdrive testing is slow, expensive. Therefore, improved methods ofdiagnosing network communication limitations are needed.

SUMMARY

Methods for providing a metric that is indicative of usage-based andcoverage-based wireless network limitations are provided. Such methodspermit identification of, for example, transmitter placement orfrequency reuse associated contributions to network error rates ordropped calls. Based upon estimates of such a metric, a network operatorcan identify possible network modifications to improve overall networkperformance.

In some examples, a distribution of call bit error rates are assigned toerror rate ranges referred to as RXQUAL ranges. Distributions aregenerally obtained for two different time period such as a time periodin which the network is busy and a time period in which the network isnon-busy. In some networks, network limitations due to reduced coveragein one or more cells or cell sectors are generally relativelyindependent of call volume, i.e., a constant fraction of calls tend toexperience coverage-based limitations for a relatively constantgeographic call distribution. Usage-based effects such as co-channelinterference tend to increase as a function of network load so thatcomparison between busy and non-busy times can be used to estimaterelative contributions of coverage and usage based effects. Receivedsignal quality values (RXQUAL) that are commonly available can be usedto produce cumulative distributions of errors for such time periods, anda relative contribution of, for example, co-channel interference can bedetermined based on a comparison of the distribution functions for thesetwo time periods.

Network characterization methods comprise establishing a performancemetric and determining values of the performance metric associated witha first time interval and a second time interval. Based on thedetermined values, a contribution of at least one network feature to atleast one of the performance metrics in at least one of the first andsecond time intervals is estimated and reported. In some examples, theperformance metric is associated with bit error rate. In other examples,the first time interval is associated with a time period during whichnetwork usage is relatively low, and the second time interval isassociated with a time period during which network usage is relativelyhigh. According to other examples, the estimated contribution isassociated with reduced-coverage zones, co-channel interference, ormultiple access interference. In representative illustrative examples,the performance metric is associated with a cumulative distributionfunction based on two or more bit error rate ranges. In some examples,the performance metric is based on received signal quality or acumulative distribution function based on two or more ranges of receivedsignal quality.

Apparatus comprise a processor configured to receive values of aperformance metric associated with a first time interval and a secondtime interval and produce an estimate of at least one of a coverage-basecontribution to the performance metric or a usage-based contribution tothe performance metric, and report the estimate. In some examples, amemory is configured to receive the estimate, and the processor iscoupled to retrieve the values from the memory. In representativeexamples, the usage-based contribution is associated with co-channelinterference or multiple access interference. In further examples, theprocessor is configured to determine a first cumulative distributionfunction based on bit error rate during the first time interval and asecond cumulative distribution function based on bit error rate duringthe second time interval, and produce the estimate based on the firstand second cumulative distribution functions. In other examples, theprocessor is configured to determine the performance metric.

Methods are provided that comprise estimating at least one of acontribution of usage-based limitations or coverage-based limitations towireless network performance. Based on the estimate, at least onewireless network element associated with the at least one estimatedlimitation is reconfigured. In other examples, a contribution ofusage-based limitations and reduced-coverage zone based limitations in awireless network are estimated, and at least one wireless networkelement is reconfigured based on the estimated contributions. In someexamples, the estimate is based on a comparison of wireless networkperformance in at least a first and a second time interval. In otherexamples, the usage-based limitations are associated with co-channelinterference, and methods further comprise modifying a frequency reusescheme based on the estimate. In other examples, a transmitter placementis adjusted or an additional transmitter is provided based on theestimate.

The foregoing and other objects, features, and advantages of thedisclosed technology will become more apparent from the followingdetailed description, which proceeds with reference to the accompanyingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a representative wireless communication networkthat includes a processor configured to estimate coverage-based andusage-based limitation to network performance.

FIG. 2 is a block diagram illustrating a representative method ofestimating coverage-based and usage-based network performancelimitations.

FIG. 3 is a graph illustrating a distribution of calls based on receivedsignal quality ranges.

FIG. 4 is a graph illustrating cumulative distribution functions ofcalls into received signal quality ranges for a busy time interval and anon-busy time interval.

FIG. 5 is a block diagram illustrating a representative computer systemconfigured to display and report estimates of coverage-based orusage-based network performance limitations.

DETAILED DESCRIPTION

As used in this application and in the claims, the singular forms “a,”“an,” and “the” include the plural forms unless the context clearlydictates otherwise. Additionally, the term “includes” means “comprises.”Further, the term “coupled” means electrically or electromagneticallycoupled or linked and does not exclude the presence of intermediateelements between the coupled items.

The described systems, apparatus, and methods described herein shouldnot be construed as limiting in any way. Instead, the present disclosureis directed toward all novel and non-obvious features and aspects of thevarious disclosed embodiments, alone and in various combinations andsub-combinations with one another. The disclosed systems, methods, andapparatus are not limited to any specific aspect or feature orcombinations thereof, nor do the disclosed systems, methods, andapparatus require that any one or more specific advantages be present orproblems be solved.

Although the operations of some of the disclosed methods are describedin a particular, sequential order for convenient presentation, it shouldbe understood that this manner of description encompasses rearrangement,unless a particular ordering is required by specific language set forthbelow. For example, operations described sequentially may in some casesbe rearranged or performed concurrently. Moreover, for the sake ofsimplicity, the attached figures may not show the various ways in whichthe disclosed systems, methods, and apparatus can be used in conjunctionwith other systems, methods, and apparatus. Additionally, thedescription sometimes uses terms like “produce” and “provide” todescribe the disclosed methods. These terms are high-level abstractionsof the actual operations that are performed. The actual operations thatcorrespond to these terms will vary depending on the particularimplementation and are readily discernible by one of ordinary skill inthe art.

In some communication networks such as, for example, wirelesscommunication networks that provide telephone and data services overlarge coverage areas, calls or other communications can be dropped orslowed or services can be unavailable because of subscriber locationrelative to network access points such as radio base stations. Forexample, a subscriber can be located at a “hole” in a network coveragearea caused by buildings or other structures situated between thesubscriber and a radio transmitter. For convenience herein, locations orareas in a network coverage area that are associated with impairednetwork communication based on their locations are referred to asreduced-coverage zones. In some examples, reduced-coverage zonescorrespond to areas in which subscriber services are unavailable, buttypically, such zones are associated with areas at which communicationwith the network is impaired, but services remain available.

Communication networks such as wireless communication networks alsoexhibit limitations based on numbers of subscribers using or requestingservices, or numbers of communications requested or being serviced. Forexample, a wireless network subscriber can experience degraded networkservices due to service requests by other subscribers, particularly ifall the service requests originate at or near a common location or use acommon frequency channel. For convenience, such communicationlimitations are referred to herein generally as usage-based impairments.Such usage-based impairments can include those associated with a limitednumber of frequencies or time slots in a particular cell, orinterference with communications at a common (reused) frequency in adistant cells such as prescribed by a frequency reuse plan. In otherexamples, such impairments are associated with increasing numbers ofusers in a wireless network based on code division multiple access(CDMA) and can be referred to as multiple access interference.

In representative examples described herein, applications of thedisclosed technology to cellular networks based on frequency divisionmultiple access (FDMA) and time division multiple access (TDMA) such asGSM networks as well as CDMA based networks such as those specified bythe IS-95 standard are described. These network configurations arechosen for convenience only, and other FDMA/CDMA-based or other networkscan be similarly evaluated for reconfiguration.

Referring to FIG. 1, a wireless communication network 100 includes aplurality of mobile stations 102A-102D, each of which is configured forwireless communication with one or more of a plurality of basetransceiver stations (BTS) 104A-104C that are associated with respectivecells 105A-105C. In a typical network, a plurality of cells establish anetwork coverage area in which wireless services are generallyavailable. In some wireless communication networks based on standardssuch as the Digital Advanced Mobile Phone System (D-AMPS) and the GlobalSystem for Mobile Communications (GSM), each BTS is allocated aparticular set of frequency bands on which it transmits and receives.The cells 105A-105C can be divided into sectors and each sectorallocated a subset of frequency bands selected from the set allocated tothe BTSs 104A-104C, respectively. For example, if the cell 105C isassigned nine frequency bands f₁, . . . , f₉, sectors 107A-107C can beassigned frequency subsets f₁-f₃, f₄-f₆, and f₇-f₉, respectively.Because of limitations of available spectrum, the frequency bands f₁, .. . , f₉ are used (i.e., “reused”) in one or more other cells, andgenerally assigned to sectors in a similar manner.

A base station controller (BSC) 106 is coupled to the BTSs 104A-104C andgenerally coordinates communications with the BTSs 104A-104C. Forexample, the BSC 104 can coordinate frequency allocation with the mobilestations. The BSC 104 can also coordinate hand-off of calls betweencells as the mobile stations move. A mobile switching center (MSC) 108can be coupled to the BSC 104 and other BSCs. The MSC 108 coordinatescommunications between mobile stations and between mobile stations and apublic switched telephone network (PSTN) 110 that provides access to aglobal telecommunications network or other communication networks. TheMSC 108 can also coordinate hand-off.

An available frequency spectrum can be allocated to the cells or acoverage area in various ways. Some exemplary networks useFrequency-Division Multiple Access (FDMA), wherein an allocated radiofrequency spectrum is divided into a plurality of sub-bands. Examples ofsuch standardized networks include AMPS for analog systems and DAMPS andGSM digital systems. DAMPS and GSM use FDMA in conjunction withTime-Division Multiple Access (TDMA), wherein the frequency sub-bandsprovided by DAMPS or GSM are divided into time slots. Other allocationsof frequencies are possible, and the disclosed technology is not limitedto any particular frequency assignment scheme. In addition, as discussedbelow, in some examples, a radio frequency spectrum assigned to anetwork operator is not divided into bands, sub-bands, or sets offrequency bands, and communications are distinguished based on a codeassigned to a particular device or communication.

One or more network elements such as the BSCs or MSC of FIG. 1 can beconfigured to record network communication statistics as a function oftime for use in assessing network performance and identifying potentialareas for network reconfiguration. For example, numbers of calls orother communications having selected bit error rates can be recorded asa function of time. Based on the recorded numbers, network performancelimitations can be associated with reduced coverage-zones or asusage-based limitations as described below. As shown in FIG. 1, suchdata is stored in a memory 120, and coupled to a processor 122 foranalysis.

With reference to FIG. 2, a representative method is illustrated. In astep 202, a bit error rate or other call or data connectioncharacteristic is measured for a plurality of calls or othercommunications in a first time interval and in a selected coverage area.The bit error rate can be recorded for some or all communications oralternatively, a bit error rate for a particular communication can beassigned to one of a set of predetermined bit error rate ranges so thata total count of calls having a bit error rate in one or more of theranges can be established. In a representative example, a set ofreceived signal quality (RXQUAL) ranges are established, wherein theRXQUAL ranges are based on call bit error rates. Bit error rates foreach of a set of calls can be assigned to one of the RXQUAL ranges basedon the call bit error rate, and a first distribution of calls as afunction of bit error rate range (RXQUAL ranges) during the first timeinterval is obtained in a step 204. Call bit error rate is typicallymeasured about every 480 ms, so that any call can contribute a number ofsamples to the RXQUAL ranges.

In a step 206 a bit error rate or other characteristic is recorded for aplurality of calls in a second time interval. The bit error ratesassociated with call measurements can be assigned to the RXQUAL ranges,and a second distribution of calls obtained in a step 208. Typically thefirst time interval is selected so that the network is relatively“non-busy” during the first time interval, and the second time intervalis selected so that the network is relatively busy during the secondtime interval. For many wireless networks, non-busy times can beassociated with late night hours (1-3 AM) or very early morning hours(4-6 AM), and busy times can be associated with late afternoon hours(4-6 PM). Based on the first and second distributions, associated firstand histograms can be obtained by normalizing the distributions based ona total number of calls.

In a typical example, eight RXQUAL BER ranges RXQUAL_(n), wherein n=0, .. . 7, are provided, wherein n=0 corresponds to calls having a highestquality (lowest bit error rate). Increasing values of the integer indexn are associated with progressively poorer received signal quality. Aconvenient set of RXQUAL ranges is illustrated in the following table.

RXQUAL Ranges RXQUAL_(n) Bit Error Rate (BER) Range 0  0.0% ≦ BER < 0.2%1  0.2% ≦ BER < 0.4% 2  0.4% ≦ BER < 0.8% 3  0.8% ≦ BER < 1.6% 4  1.6% ≦BER < 3.2% 5  3.2% ≦ BER < 6.4% 6  6.4% ≦ BER < 12.8% 7 12.8% ≦ BERThe threshold levels establishing each bin are typically determinedusing mean-opinion-score (MOS) evaluations, where an MOS less than 3 isconsidered a degraded signal. Methods associated with so-called“Perceptual Evaluation of Speech Quality” as specified in, for example,ITU-T Recommendation P.862 can be used to select a suitable thresholdlevel.

Once RXQUAL ranges are selected and numbers of call samples in each ofthe ranges have been obtained as a set of values RXQUAL_(n), acumulative distribution function CDF can be determined as a function ofn to yield a percentage of call samples that have a BER (and anassociated signal quality) at least as poor as that associated withRXQUAL_(n) in a selected time interval T:

${{{CDF}\left( {n,T} \right)} = \frac{\sum\limits_{i = n}^{7}\;{RXQUAL}_{i}}{\sum\limits_{i = 0}^{7}{RXQUAL}_{i}}},$wherein i is an integer. While it can be convenient to obtain values ofthe CDF for all ranges (i.e., for all values of n), in some examples oneor a few values can be selected to provide an indicator of networkperformance in one or more time intervals.

The start and stop times of the first time interval (T₁) can be selectedso as to reduce or minimize effects of network load, thereby reducing,minimizing, or eliminating call degradations associated with co-channelinterference or other network traffic-based degradations. Thus, in sucha time interval, call degradations can be associated with networkcoverage limitations or other network architecture limitations that areindependent of network traffic volume. As noted above, for a typicalwireless cellular telephone network, a time period during early morninghours often is suitable such as from about 4 AM to about 5 AM. Starttime and duration can be selected based on a particular network'straffic patterns.

A second histogram is generated for a time interval associated with arelatively heavy network traffic, and a CDF (or a partial CDF) based oncall samples placed during this time interval is computed and comparedwith a similar CDF for the non-busy time interval in a step 210.Selection of a start time and duration can be selected to correspond toperiods of peak network traffic or other period. If a peak traffic timeis selected, then the associated CDF can include a largest anticipatedcontribution to call degradation produced by co-channel interference orother traffic based degradations. In other examples, other periods ofmoderate usage between peak usage and minimum usage can be monitored toyield a contribution of co-channel interference or other networkusage-based limitation as a function of network load. In some examples,CDFs for a plurality of time intervals can be obtained so thatcontributions to call degradation from network traffic dependent sourcessuch as co-channel interference can be estimated. Alternatively, normalnetwork traffic variations at a common time of day can be used todetermine relative contributions of coverage-based and traffic-basedlimitations. For example, day to day variations in CDF at a selectedtime of day can be correlated with variations in total traffic at theselected time of day.

In other examples, call or other communication data collected at acommon time of day can be used to estimate usage-based limitations andlimitations associated with reduced-coverage zones by recording ageographic distribution of calls or recording frequency assignments. Insuch an example, increases in error rates associated with more compactgeographic distributions or higher rates of reuse of particularfrequencies can be associated with usage-based limitations such asco-channel interference. Typically such data is stored in a memory forready access, or selected values of the associated distributionfunctions can be recorded.

In the example of FIG. 2, a contribution of co-channel interference orreduced-coverage limitations for a given call quality can be determinedin a step 212 by, for example, subtracting the computed non-peak CDFfrom the CDF computed for a period of higher network load. If therelative geographic distribution of callers remains approximatelyconstant, the additional contribution to the percentage of calls fallingbelow a given RXQUAL level during a high network load period as comparedto low network load period can be associated with one or moreusage-based limitations. Typical examples of such limitations includeco-channel interference in FDMA systems, or multiple access interferencein CDMA systems. As used herein, co-channel interference includesinterference based on reuse of the same frequency channel, interferencebetween adjacent or relatively close channels, and other frequencyrelated interference.

FIG. 3 is a graph illustrating a representative distribution of callsinto RXQUAL ranges. Distributions such at that of FIG. 3 can beprocessed to produce CDFs or other assessment metrics. FIG. 4illustrates results of a representative network assessment based on calldistributions according to a method such as that of FIG. 2. As shown inFIG. 4, cumulative distribution functions for a busy and non-busy timeperiod are graphed as a function of RXQUAL ranges. An increase in theCDF for a given RXQUAL that is associated with the busy time can be usedas an estimate of a relative contribution of usage-based limitations tooverall network performance. As illustrated in FIG. 4, contributions ofreduced-coverage zones and co-channel interference are approximatelyequal. In some examples, contributions are substantially different. Asshown in the FIG. 4, the relative contributions of reduced-coveragezones and usage-based limitations are approximately constant as afunction of RXQUAL range, but in other differences, the differences arefunctions of RXQUAL.

In other examples, BER measurements associated with selected groups ofcells can be used to assess co-channel interference or other networklimitations for the selected portion of a coverage area. In this way, anetwork operator can pinpoint specific areas of a wireless network whereeither co-channel interference is excessive or reduced-coverage zonesappear to be limiting network performance so that appropriate remedialmeasures can be implemented.

Turning to FIG. 5, a representative typical computer system 500 suitablefor estimating and reporting usage-based or coverage-based networkperformance characteristics includes a central processing unit (CPU) 502that is in communication with a system bus 504. A memory 506 is coupledto the system bus 504 and can include read-only memory (ROM) 510 andrandom-access memory (RAM) 508. Other computer readable media can alsobe included such as a storage device 512 that stores computer-executableinstructions for delivery to the CPU 502. The storage device 512 can bea hard disk, a floppy disk, CD ROM, or other storage device, or someportions of the memory 506 can be configured to store such instructions.A network interface 514 is provided for communication with a networksuch as a wireless network in order to receive network statistics suchas RXQUAL-based call distributions or other data or distributions. Auser input device 516, such as a mouse or keyboard, is provided for userselection of network characteristics to be monitored or processed, timeintervals in which call or data communication characteristics are to beaccumulated, or other data collection or network assessment parameter. Adisplay 520 is generally provided to report network performanceevaluations to a network technician.

In some examples, a user menu is presented on the display 520 to aid inselection of time intervals in which bit error rate range counts orother measurements are to be obtained. Such a user interface can alsoprovide entries associated with selection of other network operationaldata such as numbers of dropped calls, effective data rate for aparticular call or an average effective data rate, data latency, biterror rate, or other network characteristics that can be used to produceappropriate network statistics for distinguishing coverage andtraffic-based network limitations. Typically, any statistical or othermeasured or computed values can be reported by display on the displaydevice 520, stored in a memory, or otherwise presented to networkpersonnel for additional network planning or to aid in networkreconfiguration. For example, coverage-based or traffic-basedprobabilities for dropping calls in one or more cells can be displayed,or a list of cells exhibiting predominately coverage-based ortraffic-based communication can be provided. Once the relativeimportance of coverage and traffic-based limitations have been assessed,some cells or other network portions can be identified for additionalradio towers or relocation of an existing tower. Alternatively,frequency assignments can be altered to reduce co-channel interferenceif co-channel interference is determined to be a signification networklimitation.

While FIG. 5 illustrates a stand-alone computer system, such a systemcan be distributed throughout a wireless network or other network orsituated at a single network node. Network elements such as mobilestations can be configured as shown in FIG. 5, and a dedicated system isnot required. For example, the computer system can be based on networkelements of a wireless communications network, including mobilestations, ground stations, ground station controllers, or networkswitching or monitoring systems. Bit error rate, bit error rate ranges,or other network performance parameters can be measured, stored, andcommunicated from one or more such network elements, or communicated viathe Internet or other network to another processing system for storage,display, and identification of potential network reconfigurations basedon likely sources of call errors.

Representative examples presented above are based on bit error rates ofcalls on wireless networks that use FDMA. In some network architecturesFDMA is not used, but the disclosed technology permits differentiationof traffic capacity based limitations and coverage-based limitations inother networks as well. For example, in a wireless network based on aso-called Code Division Multiple Access (CDMA), mobile stations aretypically assigned a unique code but transmit and receive over a sharedradio frequency spectrum. As network traffic increases, so-calledmultiple access interference (MAI) increases due to the presence ofcommunications based on increasing numbers of codes. Thus, asignal-to-interference ratio tends to decrease as a number of usersincreases. In CDMA-based networks, coverage-based or usage-basedcommunications limitations such as dropped calls can be identified byassessing network performance during busy and non-busy time intervals.

Network characterization can be based on voice calls or othercommunications such as data communications or text messaging. Inaddition, other call or communication quality indicators can be usedsuch as, for example, effective bit rate, latency, or other indicatorsAs noted above, during non-busy time intervals, coverage limitations arelikely to be apparent while in busy time intervals, usage-basedlimitations are likely to be apparent. While it can be convenient toassess network performance based on busy and non-busy time intervals,any two time intervals having different usages can be used. A comparisonof network performance based on, for example, cumulative distributionfunctions, for different time intervals can provide an estimate ofcontributions of coverage-based or usage-based limitations.

In view of the many possible embodiments to which the principles of thedisclosed technology may be applied, it should be recognized that theillustrated embodiments are only representative examples and should notbe taken as limiting. We therefore claim as our invention all that comeswithin the scope and spirit of these claims.

What is claimed is:
 1. A method for estimating a level of contributionof an interference to a performance metric in a wireless network, themethod comprising: establishing, by a processor, the performance metric,wherein the performance metric comprises a number of droppedcommunications; determining, by the processor, a value of theperformance metric associated with a first time interval and a value ofthe performance metric associated with a second time interval, whereinthe first time interval is associated with a time period during whichnetwork usage is low as compared to the second time interval, and thesecond time interval is associated with a time period during whichnetwork usage is high as compared to the first time interval; producing,by the processor, an estimate of the level of contribution of theinterference to the performance metric in the second time interval, bysubtracting the value of the performance metric associated with thefirst time interval from the value of the performance metric associatedwith the second time interval, wherein the interference comprises aco-channel interference; and reporting, by the processor, the estimateof the level of contribution of the interference to the performancemetric in the second time interval.
 2. The method of claim 1, whereinthe number of dropped communications comprises a number of droppedcalls.
 3. The method of claim 1, wherein the number of droppedcommunications comprises a number of dropped data communications.
 4. Themethod of claim 1, wherein the number of dropped communications is basedon a single cell.
 5. The method of claim 1, wherein the number ofdropped communications is based on a plurality of cells.
 6. The methodof claim 1, further comprising: assessing, by the processor, whether thenumber of dropped communications is attributable to a coverage-basedlimitation.
 7. The method of claim 1, further comprising: assessing, bythe processor, whether the number of dropped communications isattributable to a usage-based limitation.
 8. The method of claim 1,wherein the performance metric is based on a received signal qualityassociated with the number of dropped communications.
 9. The method ofclaim 8, wherein the performance metric is a cumulative distributionfunction based on two or more ranges of the received signal quality. 10.An apparatus, comprising: a processor; and a computer-readable mediumstoring instructions which, when executed by the processor, cause theprocessor to perform operations, the operations comprising: receiving avalue of a performance metric associated with a first time interval anda value of the performance metric associated with a second timeinterval, wherein the performance metric comprises a number of droppedcommunications in a wireless network, wherein the first time interval isassociated with a time period during which network usage is low ascompared to the second time interval, and the second time interval isassociated with a time period during which network usage is high ascompared to the first time interval; producing an estimate of a level ofcontribution of an interference to the performance metric in the secondtime interval by subtracting the value of the performance metricassociated with the first time interval from the value of theperformance metric associated with the second time interval, wherein theinterference comprises a co-channel interference; and reporting theestimate of the level of contribution of the interference to theperformance metric in the second time interval.
 11. The apparatus ofclaim 10, wherein the number of dropped communications comprises anumber of dropped calls.
 12. The apparatus of claim 10, wherein thenumber of dropped communications comprises a number of dropped datacommunications.
 13. The apparatus of claim 10, wherein the number ofdropped communications is based on a single cell.
 14. The apparatus ofclaim 10, wherein the number of dropped communications is based on aplurality of cells.
 15. The apparatus of claim 10, the operationsfurther comprising: assessing whether the number of droppedcommunications is attributable to a coverage-based limitation.
 16. Theapparatus of claim 10, the operations further comprising: assessingwhether the number of dropped communications is attributable to ausage-based limitation.
 17. The apparatus of claim 10, wherein theperformance metric is based on a received signal quality associated withthe number of dropped communications.
 18. The apparatus of claim 17,wherein the performance metric is a cumulative distribution functionbased on two or more ranges of the received signal quality.
 19. Amethod, comprising: estimating, via a processor, a level of contributionof an interference to a performance metric in a wireless network,wherein the performance metric comprises a number of droppedcommunications, wherein the interference comprises a co-channelinterference, wherein the estimating is based on a comparison of a valueof the performance metric in a first time interval and a value of theperformance metric in a second time interval, wherein the estimatingcomprises subtracting the value of the performance metric associatedwith the first time interval from the value of the performance metricassociated with the second time interval, wherein the first timeinterval is associated with a time period during which network usage islow as compared to the second time interval, and the second timeinterval is associated with a time period during which network usage ishigh as compared to the first time interval; and based on the level ofcontribution that is estimated, reconfiguring a wireless networkelement.
 20. The method of claim 19, further comprising: modifying afrequency reuse scheme based on the level of contribution that isestimated; adjusting a transmitter placement based on the level ofcontribution that is estimated; or adding an additional transmitterbased on the level of contribution that is estimated.